Switching mode power supply (SMPS) is widely used in portable electronic equipments. The SMPS has at least one switch, and for many reasons, the SMPS has a parameter of minimum on time Tmin which is defined as the minimum on time of the switch in one period. For example, the inherent signal delay of the logic circuit and the driver circuit in the SMPS causes the SMPS to have the minimum on time Tmin. Or in order to prevent false trigger of the switch, the designer sets the minimum on time Tmin for the SMPS on purpose. Recently, on one hand, the decreasing power dissipation of the portable electronic equipments requires a decreasing output voltage of the SMPS. On the other hand, the input voltage range of the SMPS should increase for broader application. So in the practical application, it is very common to require a SMPS has a high input voltage together with a low output voltage, thus the required on time of the SMPS becomes very small. In such a condition, when the required on time of the SMPS is smaller than the minimum on time Tmin, an over voltage issue will happen.
In light of the above description, a method is needed to solve at least one of the above problems.